Mechanical ventilatory parameters guided by the low flow pressure-volume curve in patients with acute lung injury/acute respiratory distress syndrome

Background: Mechanical ventilation may contribute to lung injury and then enhance systemic inflammation. Optimal ventilatory parameters such as tidal volume (V-T) and positive end expiratory pressure (PEEP) can be determined using different methods. Low flow pressure volume (P/V-LF) curve is a useful tool to assess The respiratory system mechanics and set ventilatory parameters. Aim: To set V-T and PEEP according P/V-LF curve analysis and evaluate its effects on gas exchange and hemodynamic parameters. Materials and methods: Twenty seven patients underwent P/V-LF within the first 72 hours of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). P/V-LF curves were obtained from the ventilator and both lower and upper inflexion points determined. Gas exchange and hemodynamic parameters were measured before and after modifying ventilator settings guided by P/V-LF curves. Results: Ventilatory parameters set according P/V-LF curve, led to a rise of PEEP and reduction of V-T. 11.6 +/- 2.8 to 14.1 +/- 2.1 cm H2O, and 9.7 +/- 2.4 to 8.8 +/- 2.2 mL/kg (p < 0.01). Arterial to inspired oxygen fraction ratio increased from 159.0 +/- 66 to 188.5 +/- 68.5 (p < 0.01), and oxygenation index was reduced, 13.7 +/- 8.2 to 12.3 +/- 7.2 (p < o.05). Cardiac output and oxygen delivery index (IDO2) were not modified. Demographic data, gas exchange improvement and respiratory system mechanics shouwed no significant differnece between patients with extra-pulmonary and pulmonary ALI/ARDS. There was no evidence of significant adverse events related with this technique. Conclusion: P/V-LF curves information allowed us to adjust ventilatory parameters and optimize gas exchange without detrimental effects ono oxygen delivery in mechanically ventilated ALI/ARDS patients.